[libvirt] [PATCH v6 00/13] PCI passthrough support on s390

[Andrea Bolognani]

On Fri, 2018-10-12 at 16:04 +0100, Daniel P. Berrangé wrote:
> On Fri, Sep 28, 2018 at 04:46:13PM +0800, Yi Min Zhao wrote:
[...]
> >   <hostdev mode='subsystem' type='pci'>
> >     <driver name='vfio'/>
> >     <source>
> >       <address domain='0x0001' bus='0x00' slot='0x00' function='0x0'/>
> >     </source>
> >     <address type='pci' domain='0x0000' bus='0x00' slot='0x01' function='0x0'>
> >       <zpci uid='0x0003' fid='0x00000027'/>
> >     </address>
> >   </hostdev>
> 
> I'm not sure if this was discussed in earlier versions, but to me
> this use of a child element looks wrong.
> 
> What we're effectively saying is that s390 has a different addressing
> scheme. It happens to share some fields with the current PCI addressing
> scheme, but it is none the less a distinct scheme.
> 
> IOW, I think it should be
> 
>    <address type='zpci' domain='0x0000' bus='0x00' slot='0x01'
>                         function='0x0' uid='0x0003' fid='0x00000027'/>
> 
> Of course internally we can still share much logic for assigning the
> addreses between "pci" and "zpci".

So what happens with PCI devices on s390 is that *two* devices will
be added to the guest: one is the usual virtio-net-pci or what have
you, which has its own PCI address allocated using the same algorithm
as other architectures; the other one is a '-device zpci', which IIUC
works basically like an adapter between the PCI device itself and the
guest OS, and which is identified using uid and fid.

Calling it a completely different address type seems like a bit of a
stretch: there is definitely a PCI address involved, which is why the
zPCI part was implemented through a potentially reusable "PCI address
extension" mechanism.

-- 
Andrea Bolognani / Red Hat / Virtualization